This invention relates to a microporous composite sheet material. More particularly, the invention relates to a composite sheet material which is permeable to moisture vapor but which forms a barrier to the passage of water. The composite sheet material has strength and barrier properties which make it suitable for use as a housewrap.
Various types of sheet materials have been used in the construction of buildings as a barrier fabric to block water and air while allowing transmission of moisture vapor from the building interior. These so-called housewrap products are typically applied over the sheathing layer of the building and beneath the exterior surface layer of brick or siding. During the time that the building is under construction, the housewrap material is exposed to the elements for a considerable period of time. Therefore, the fabric must have good weatherability, relatively high tear strength and puncture resistance. The fabric must also maintain the strength and barrier properties while it is exposed to the elements, and subsequently during the lifetime of the building.
Various types of fabrics have been produced and sold commercially for use as a barrier fabric in building construction. One such commercially available product is manufactured and sold by DuPont under the trademark Tyvek® Homewrap®. This product is formed from flash spun high-density polyethylene fibers which are bonded together to form a nonwoven sheet material.
Other commercially available housewrap products have been developed which utilize preformed microporous films laminated to a reinforcing substrate, as described for example in Sheth U.S. Pat. No. 4,929,303 or Martz U.S. Pat. Nos. 5,656,167 and 6,071,834.
Still other commercially available housewrap products have used a woven or nonwoven substrate with a perforated film coating. For example, in Dunaway et al. U.S. Pat. No. 4,898,761, a barrier fabric is disclosed in which a polymer film is laminated to a nonwoven fabric, and the resulting composite sheet material is then needle-punched to provide micropores through the film. The nonwoven fabric is a spunbonded web formed of polyolefin filaments, and the polymer film can be applied to the nonwoven web by hot cast extrusion.
The currently available housewrap materials have various deficiencies. Many of the commercially available housewrap materials can be easily torn when installed during construction or punctured by ladders or scaffolding leaning against the building. These materials are also susceptible to being torn by the wind during construction while the housewrap material remains exposed. Housewrap materials formed from laminates of a microporous film with a supporting substrate require a two-step process which increases the expense, and the resultant products suffer from low puncture strength and generally low overall tear and tensile strength.
The need exists for an economical barrier material with superior strength and tear resistance, as well as excellent water and air barrier properties.